Gabes Love Tub	Home of the Missing Information mod and beginning of the Obsidian Mod.
Interlopers	Interlopers, the Number one resource for learning how to map.
Valve Developer Wiki	Valve Developer Wiki, Tutorials, etc..
Half-Life Improvement	Half-Life Improvement website. Specializes in making Half-Life and Half-Life 2 a better place.
Obsidian Conflict Wiki	Obsidian Conflict Wiki. Information and tutorials about various OC-related things and features.